Male mosquito fish are livebearers and scientists have shown in experiments that females prefer males with larger genitalia.

This preference has led to the males evolving much larger private parts than many other livebearers.

However, having enormous genitals make the males more vulnerable to predators as they make swimming more cumbersome.

This means that there’s an “evolutionary trade-off” for the male mosquito fish in avoiding predators and having smaller genitals, or attracting ladies with a bigger a larger gonopodium but placing themselves at greater risk of predation.

This item was first published in the September 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.